1. Field of the Invention
This invention is generally directed to a process of precision molding glass surfaces to achieve desired optical qualities and, more particularly, to a low cost tooling replication technique for the manufacture of lens arrays and other complex optical surfaces.
2. Description of the Prior Art
The technology which gave rise to the subject invention is the technology of light valve projectors of the Schlieren dark field type. The principles and mechanisms of such light valve projectors are taught, for example, in U.S. Pat. No. 3,437,764 to Good et al. These light valve projectors include a lens system comprising an input window and an imaging lens which focuses filtered light from a high intensity lamp onto an input bar plate. The lens system comprises two arrays, each of which contains over 800 very small lenslets, which are accurately aligned to achieve the required focus of the arc light image within a transparent area of the input bar plate.
These lens arrays have been manufactured in the past by means of a precision machined stainless steel tool which is used in a glass press to form the lens arrays in molten glass. The tool is costly and time consuming to make, even when using numerically controlled machining techniques. The machined part must be hand polished to produce the final highly polished surface which has generally been considered necessary to produce a glass surface of the required optical qualities.
The process for producing the lens arrays, which comprise the input window and the imaging lens of light valve projectors of the Schlieren dark field type, is one of the contributing factors as to why the cost of these projectors has remained high for so many years. Many efforts have been made in the past to reduce the cost of manufacture of various components of light valve projectors, and great progress has been made in accomplishing this objective. However, what is needed is a method of producing lens array glass pressing tools in a cost and time efficient manner so that, in volume production, several such tools can be employed.
The technique of making a master mold which is used to make replicas by a plating process is the basic technique which is used in the phonograph record industry to make their plastic pressing molds. Plastic, however, is worked at a much lower temperature and is less abrasive than glass. Thus, the technique has not been applied to the glass pressing business. In fact, the prevailing wisdom in the glass industry is that only cast or machined tools can be used with success. In the case of a pressing where the mold costs are high and the mold life is not a major concern, i.e., a short manufacturing run of a thousand pieces versus a million pieces, the need for an inexpensive fast turn around method of generating glass pressing tools is important.